Fractionating hydrocarbon



Patented June 5, 1928.

UNITED STATES 1,672,849 PATENT OFFICE.

WARREN K. LEWIS, OE NEWTON, MASSACHUSETTS, AND ALFRED A. WELLS, OF RO- SELLE PARK, NEW JERSEY, ASSIGNORS TO STANDARD OIL rm, A CORIORATION OF DELAWARE.

DEVELOPMENT CQM- EBACTIONATING HYDBO CARBON.

No Drawing.

This invention relates to the separating of hydrocarbons, and more particularly separations where much overlapping in successive distillate fractions is not desired.

In attempting to separate hydrocarbons, obstacles are encountered by reason of the peculiar attractional force existent between the molecules. Moreover, while in the case of alcohols, esters, etc., fractionation is con- 1 cerned only with a few boiling points or constant boiling point mixtures, in the case of hydrocarbons on the other hand there are a legion of compounds of very close boiling points. In the past, hydrocarbon distillers,

particularly petroleum refiners, have accepted the conditions as constituting fixed limitations necessitating quite incomplete separations, even where re-distilling with the best equipment at hand.

In accordance with the present invention -we establish working conditions such that the difference or range between the vapor pressures of the compounds concerned is increased, and then apply conditions favoring 2 selective separations. The primary principle involved may be made clear by illustrations;

., thus, while for instance at 248 F. n-hexane is about twelve times more volatile than n decane, at 68 F. it is about forty-four times morevolatile; and for example in the case of aromatic com ounds, while for instance benzol at 230 is about 2.3 times more volatile than toluol, at 86 F. it is about 3.2 times more volatile. In the practice of our invention, we secure increased ease of separation by increasing the differences in relative volatility'through lowerin the operating boiling point, .as far as easible, this being accomplished by lowering the working 40 pressure, thatis by application of vacuum; and the vapors which are boiled ofi are then subjected to a rectifying action or counter-current intermingling and washing through progressively cooler zones with condensed fractions resulting from the cooling -of the vapor current further along in its course. Any suitable type of apparatus can be used, for instance thevapors are passed through a plate and bell type of column, or a so tower having plates perforated with such size openings as to allow some accumulation of condensate on the plates for the vapors to successively bubble through, or any con- Application filed March 5, 1924. Serial No. 697,135.

struction allowing an adequate washing or interchange.

As showing the character of action occurring, the following experimental data may be noted:

A mid-continent petroleum distillate of 382 B. was fractionated in a plate and bell-cap column, and 10% cuts taken, in the first instance at atmospheric pressure and in the second instance, (using the same column with the same amount of reflux), under a pressure of around 27 mm. of mercury. The respective cuts were then inspected by the usual laboratory methods, to determine their gravity and boiling range. The 10% point and 90% for each out are given in the following table, being more accurate than the initial and final.

Atmospheric Vacuum a. o. as s i s a 3 :1 0 i i 2 8 2 0 i3 3 8 53 o .11---- 48.5 347 F 434 F. 87 44 48.8 340 F 308 F. 58 12 2---- 45.7 390 464 74 57 47.7 386 440 54 34 44.7 407 484 77 54 44.7 406 453 47 15 4--.. 43.5 430 498 68 34 43.5 438 485 47 28 41.1 464 532 68 64 41.1 457 498 41 13 6---- 40.9 468 538 70 48 40.9 485 523 3B 22 7---- 40.0 490 548 58 38 39.9 501 542 41 S 8---- 38.7 510 569 59 36 39.0 534 570 36 8 9.--- 37.9 533 588 37.9 562 596 34 of the process: A distillate of about 38 B.

gravity taken from mid-continent petroleum by ordinary refinery condensing equipment was redistilled, using a plate and bell-cap column for fractionating and under an operating ressure of around 30 mm. of mercury. Contained kerosene hydrocarbons were taken ofi as vapors from tho-to of the rectifying column, while the strippe gas oil was taken off as liquid from the bottom.

By applying our invention with the stills used in primary distillation, a reduction can be efiected in heat consumption or'in the equipment necessary or' both, and we contemplate in general, where hydrocarbons are to be fractionated, the carrying out of the separation through increasing the difference in the relative volatility of theconstituents to be separated. Distillation can be conducted either batchwise, the successive cuts of distillate being progressively taken as desired, from lightest on to heaviest, or in distillation in a continuous battery where each unit is run to fractionate off one cut, the successively heavier distillates being furnished by the successive units in the battery.

The practicable extent of lowering of the operating boiling point, or lowering of the working pressure, naturally depends in large measure upon the particular hydrocarbons being separated and the sharpness of separation desired. The operating pressure may advantageously be lower in the case of heavier hydrocarbons, for example lubricating cuts for high flash and viscosity, than with ate and bubbling the vapors through pro gressively cooler zones counter-currently into washing contact with condensate produced by the cooling of the vapors further along in course, while maintaining an operating pressure of around 30 mm. of mercury.

WARREN K. LEWIS. ALFRED A. WELLS. 

